1. Field of the Invention
The present invention relates to a variable compression ratio apparatus, and more particularly, to a variable compression ratio apparatus for varying a compression ratio of mixed gas inside a combustion chamber according to an operation state of an engine.
2. Description of Related Art
In general, when a compression ratio is high, thermal efficiency of a heat engine increases, and when an ignition timing advances to a predetermined level in a case of an ignition engine, thermal efficiency increases. However, when the ignition timing advances at a high compression ratio in a spark ignition engine, abnormal combustion is generated to cause damage to an engine. Accordingly, there is a limit in ignition timing advance, and it is necessary to bear output deterioration due to the limit.
The variable compression ratio (VCR) apparatus is an apparatus for changing a compression ratio of mixed gas according to an operation state of an engine. According to the variable compression ratio apparatus, fuel efficiency is improved by increasing a compression ratio of the mixed gas in a low load operation condition of the engine, and knocking generation is prevented and engine output is improved by decreasing the compression ratio of the mixed gas at a high load operation condition of the engine.
The variable compression ratio apparatus in the related art implements a change in a compression ratio by changing a length of a connecting rod connecting a piston and a crankshaft. In such a type of variable compression ratio apparatus, a part connecting the piston and the crankshaft is formed of several links, so that combustion pressure is directly transmitted to the links. Accordingly, durability of the links deteriorates.
As the results of various experiments for the variable compression ratio apparatus in the related art, it is revealed that operation reliability is improved by changing a distance between a crank pin and a piston pin by using an eccentric bearing.
A plurality of links is used in order to rotate the eccentric bearing, and there is a problem in that when the links are horizontally widened or separated when the piston descends. In the related art, a separate apparatus needs to be included in the connecting rod or the link in order to confine a movement trajectory of the link, so that there is a problem in that a structure of the connecting rod or the link is complicated.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.